Approaches To Solving Constraint Dimensions Of Combined Entity

Intelligentization and automation of dimensioning is an important part of CAD/CAPP/CAM, but due to the multiplicity of entity and flexibility of allocating dimensions, the problem of constraint dimensions has not been solved perfectly. Constraint dimensions can give a numerical standard for testing completeness of 2D engineer graphics dimensioning.In this paper, based on analyzing the forming regularity, geometric characteristic and dimensioning factor of primitive and combined entity, the notion of explicitly feature position of geometric shape of primitive is introduced, the classification is dicussed. The notion of explicitly feature position constraint of geometric shape of combined entity is introduced. The classification, the explicitly reductive property for location dimension, the constraint of the explicitly feature position constraint of geometric shape of combined entity degree are systematically analyzed. To solving the constraint dimensions, a new strategy appending the location dimension beforehand is applied, and the formula to solving the constraint dimensions is established. The algorithms to testing the feature position constraint are brought forward, and obtain the constraint dimensions of the combined entity.Firstly, the geometric and dimension characteristic of different feature primitive is analysed. The notion of explicitly geometric shape feature position of primitive is introduced, and the classification of explicitly geometric shape feature position is studied carefully. Secondly, taken the combining principle of combined entity as the basis, the notion of explicitly geometric shape feature position constraint of combined entity is introduced. The classification - the explicitly reductive capacity to location dimension, constraint degree, dividing constraint level of explicitly geometric shape feature position constraint are systematically studied. In the following, based onthat theories analysis and the 3D space of primitive and combined entity is existed, a new strategy appending the location dimension beforehand is applied, and the formula to solving the constraint dimensions is established. The algorithms to testing the feature position constraint among the primitive are brought forward. The location relationship among primitives is discriminated with the explicitly geometric shape feature position of primitive, and the constraint among the primitivescan be obtained. Finally, the constraint dimensions of combined entity can be get with that formula.To prove correctness of this approach, the development system is based on AutoCAD system, we introduced Object-Oriented technology including ObjectARX and Visual C++ in the prototype system, the system achived the aim of solution the constraint dimensions of combined entity. The result show that constraintal dimension are obtained by using this method.